Earlier quoted context omitted.
This was at his local airport in Sweden. To quote some tweets: "They denied me entry on ESTA with no explanation. Already at check-in in Sweden. =( or rather instead of check-in" "I only got to the airport locally. My passport was flagged somehow so the airline wouldn't let me check in, called to ask why... So they say" Edit: ESTA is this: https://esta.cbp.dhs.gov/esta/ So the DHS denied him for some reason.
but when you apply for an ESTA you get told you've been 'approved' - you use this as a basis for booking a flight and travelling, if they're going to take it back without telling you (they have your email address) that really sucks, kind of passive aggressive
I had to make a new one on the spot, was no problem, but it seems that they will just approve the ESTA when applying for it, and then later refuse you if they want.